Doctoral Dissertations

Date of Award

8-1976

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Plant, Soil and Environmental Sciences

Major Professor

Leonard M. Josephson

Committee Members

R. R. Shrode, Fred L. Allen, J. D. Caponetti, Vernon H. Reich

Abstract

A phenotypic recurrent selection program for low-ear placement in corn (Zea mays L.) was begun in 1961 in an early and a late maturing population involving several low-ear inbreds. Approximately 250 plants were grown in each generation of selection. The plants were divided into two equal size groups. Bulk pollen was collected from phenotypically low-ear plants of one group and used to pollinate phenotypically low-ear plants of the other group. Reciprocal pollinations were made in a similar manner. Minimum plant heights were imposed and plants flowering within a specific time span were pollinated. The total number of plants selected in each generation ranged from 15 percent to 25 percent of the total number of plants. The generations of selection were tested by regression analysis in a diallel set of crosses and in testcrosses to both high- and low-ear single cross testers. In addition, generation mean analysis was performed for two crosses involving high- and low-ear inbreds of white and yellow endosperm type. Data from the studies were obtained at Knoxville and Crossville, Tennessee during 1974 and 1975. Data obtained were ear and plant heights, plant/ear height ratio, number of leaves below and above the ear, number of days to silking and tasselling, and yield. Ear height was reduced approximately 1.25 inches per generation for both the early and late maturing synthetics. Plant height decreased only slightly resulting in an overall increase of plant/ear height ratios. There was a significant increase in the number of leaves below the ear and a significant increase in the number of leaves above the ear. The number of days from planting to silking and tasselling did not change throughout the generations of selection. Yield reductions were observed in the later generations. Significant general combining ability effects were noted for all characters indicating that selecting for lower ear placement was effective. The testcrosses showed less differences among the generations than did the generations of selection per se. Significant additive effects occurred for ear height, number of leaves below and above the ear, and plant/ear height ratio for the cross E199 X Mo18W. Significant dominance effects were noted in both crosses for plant height. Significant additive and dominance effects occurred for plant/ear height ratio in the cross T232 x T458R.

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